Traditionally, coil components such as inductors, transformers, and chokes are used in a wide variety of applications such as home electric appliances, industrial apparatuses, and vehicles. A coil component is composed of a magnetic core and a coil wound around the magnetic core. Such a magnetic core often includes ferrite, which is superior in magnetic properties, freedom of shape, and cost.
In recent years, as a result of downsizing of power supplies for electronic devices, there has been a strong demand for compact low-profile coil components operable even with a large current. Powder magnetic cores produced with a metallic magnetic powder, which has a saturation magnetic flux density higher than that of ferrite, are increasingly used for magnetic cores for such coil components. Such a metallic magnetic powder includes, for example, an Fe—Si alloy, an Fe—Ni alloy, or an Fe—Si—Al alloy.
Powder magnetic cores obtained through compaction of a metallic magnetic powder such as an Fe—Si alloy powder have high saturation magnetic flux density, but have low electrical resistivity because they are produced with a metallic magnetic powder. Therefore, methods for improving insulation between magnetic particles are used, such as forming an insulating coating on the surface of a magnetic powder and then molding the magnetic powder. Patent Document 1 discloses an example of the use of an Fe—Cr—Al magnetic powder that can produce, by itself, a high-electric-resistance material capable of acting as an insulating coating. Patent Document 1 discloses a process that includes subjecting a magnetic powder to oxidation so that an oxide coating with high electric resistance is formed on the surface of the magnetic powder and then solidifying and molding the magnetic powder by discharge plasma sintering to form a powder magnetic core.
Patent Document 2 discloses that soft magnetic alloy particles including iron, chromium, and silicon are oxidized to form an oxide layer on the surface of the particles, the content of chromium in the oxide layer is higher than that in the alloy particles, and the particles are bonded together with the oxide layer interposed therebetween.